Author(s): P. M. G. Beceiro; M. C. Almeida; J. Matos
Linked Author(s): Jorge Matos
Keywords: Computational Fluid Dynamics (CFD); Hydraulics; Air entrainment; Vertical drop; Backdrop; Sewer system
Abstract: The presence of dissolved oxygen in water flows is considered an important indicator of water quality. The incorporation of dissolved oxygen in wastewater flowing in sewer systems is a process investigated by several authors, through theoretical and experimental studies, in order to quantify the effect of continuous reaeration through the air-liquid interface or air entrained due the presence of singularities such as drops or junctions. Many additional studies exist related to water quality in natural streams. It is recognised that the presence of drops and other structures increases the incorporation of air and thus increases the dissolved oxygen concentration in wastewater. The enhancement of turbulence in the sewer, leads to significant entrainment of air bubbles in the bulk water, increases the contact surface and thus the air-water mass transfer. These structures can be useful in order to ensure the aerobic conditions in the sewer system. In the present paper a study to evaluate the hydraulic behaviour of air-water flow in sewer drops, namely a vertical drop and a backdrop, using the commercial computational fluid dynamics (CFD) code FLOW-3D is presented. Some preliminary information related to air entrainment in the outlet pipe is also included. The existence of several experimental studies, developed in a physical model, where both hydraulics and dissolved oxygen measurements were carried out, provided the opportunity to test the results from the numerical investigation.
Year: 2014